A physically typical Atlantean, Fen could lift at least 2 tons, swam at approximately 30mph, and aged much slower than humans.

Abilities

Fen could extract oxygen from the water through her gills and her body was able to withstand the extreme pressures and temperatures of the oceans depths. Her vision was exceptional in the murky sea. Like most Atlanteans Fen could not breath above the water for extended periods without the assistance of chemicals, magic potions or spells.

In early 1920, the ship "Oracle" arrived in the Antarctica, it ice-breaking explosions accidentally damaged the undersea city of Atlantis. Emperor Thakorr ordered a surveillance expedition, his adventurous daughter Fen took it upon her self to fulfill task of spy. Encouraged by Atlantean scientist Tulem, whose operatives had prompted an interest in surface man during Fen's younger years, Fen used an experimental potion, allowing her to breath above water, it is unclear if she was aware that centuries of selective eugenics, overseen by Tulem and others, made her uniquely suited for procreating with humans. Fen met ship captain Leonard McKenzie, whom Tulem's forces had manipulated via telepath, Paul Destine, causing the couple to fall in love and they rapidly married. Atlantean soldiers drove the Oracle and its crew from Antarctica, and later that year Fen gave birth to Namor.